This invention relates to a method for the production of a rim hole in hollow profiles.
A method of this general type has been disclosed by German document DE 43 22 632 A1. In this case, the hollow profile is used as a vehicle strut for the mounting of axles, wheel suspensions or the like and is shaped in a first step by hydroforming into an outer contour corresponding to the loading requirements. Then, in a second step, centering holes are incorporated at the ends of the hollow profile, which are to have a mounting seat for accommodating rubber mounts, and a spacer in the form of a tubular piece is inserted into the hollow profile centrally relative to the centering holes. Finally, a flow drill is inserted into the centering holes in the end region, with the flow drill forming a rim hole during operation, and the rim hole extending inside the tubular piece. In this case, the rim hole forms the mounting seat. However, a precondition of the flow drilling process is that there must be a certain ratio between the wall thickness of the hollow profile and the diameter, to be produced, of the rim hole. The wall thickness of the hollow profile is to be especially large in relation to the diameter. This usually cannot be maintained when applied in automobile construction, since the need to save weight leads to thinner and thinner sheets. Furthermore, due to the process, the wall thickness of the rim hole decreases to virtually zero in the direction of application during flow drilling. This has an adverse effect on the strength and rigidity properties of the mount to be produced, despite the inserted tubular piece mentioned.
The object of the invention is to develop a method of the type mentioned in which a rim hole can be made in hollow profiles in a relatively simple manner, and in which the rim hole complies with high strength requirements even in the case of a small wall thickness of the hollow profile.
The object is achieved according to the invention.
Owing to the invention, in order to produce the rim hole, it is merely necessary to punch out two opposite holes and bend over at least one of the hole edges, which are drawn into the hollow profile interior in the process and thus form the rough contour of the rim hole to be produced. In order to achieve the desired exact contour of the rim hole, a tubular piece is inserted into the hollow profile interior and placed at the location of the rim hole to be produced, before the drawing-in from the open end of the hollow profile. In this case, the inside of the tubular piece serves at least as a pattern for the desired contour of the rim hole, the hole edges being pressed against the inside of the tubular piece when they are being drawn in, as a result of which they achieve this same contour. Owing to the fact that the hole edges are not subjected to any change in wall thickness when being bent over into the hollow profile interior, the tubular design of the rim hole, in addition to the already rigid tubular form per se, has especially high rigidity, which enables the rim hole, without sustaining damage, to cope with even higher mechanical loads, for which sufficient rigidity and strength are indispensable. This is additionally promoted due to the fact that the tubular piece remains in the hollow profile. In contrast to the flow drilling, the ratio of diameter to length of the rim hole is not limited to a specific value during the production of the rim hole, so that rim holes of virtually any desired dimensions can be advantageously formed. As a result of the uniformity of the wall thickness of the hollow profile, smaller wall thicknesses may also be selected when designing the hollow profile, while maintaining sufficient rigidity in the region of the rim hole. This contributes to the reduction in weight of the corresponding component and, when the component is used in the motor vehicle, to a reduction in weight of the latter. Furthermore, the method according to the invention has an advantageous effect for the painting of the component, i.e. of the hollow profile, since the surface of the rim hole is relatively regular and thus the paint can adhere to that surface. When steel is used for forming the hollow profile, there are advantageously no corrosion problems, as are brought about, for example, as a consequence of the flow drilling process.
In a preferred development of the invention, the hollow profile is perforated by the interaction of a perforating die, pushed into the hollow profile, and two opposite perforating punches, between which the hollow profile lies. In a mechanically simple manner, this enables holes having a highly precise hole pattern to be formed and enables the hole edge to run uniformly. This ensures the uniformity of the subsequent drawing-in operation and is therefore beneficial to the process reliability of the production of the desired rim hole.
In a further, especially preferred development of the invention, the hollow profile is formed by the internal high pressure forming process and perforated in the internal high pressure forming tool required for this purpose. Here, too, a highly precise hole pattern is obtained, the holes being formed by perforating punches which act upon the hollow profile with a cutting action against the internal high pressure which prevails in the hollow profile and which functions as supporting pressure suppressing subsidence or collapse. In an economical manner in terms of the method, the hollow profile is shaped in the same tool in accordance with the requirements, thereby resulting in a production plant which is extremely compact in terms of apparatus due to the integration of the perforating punches in the internal high pressure forming tool.
In a further preferred configuration of the invention, the drawing-in operation is effected by a follow-on contour of the perforating punch, this follow-on contour adjoining a cutting edge formed on the end face of the perforating punch. Due to the arrangement of a follow-on contour on the perforating punch, the perforating and drawing-in operation is simplified and the production time for the rim hole is reduced, since the hollow profile has to be acted upon, at least from one side, merely by a perforating punch which is lowered further into the hollow profile interior in a simple manner, so that the follow-on contour of the perforating punch comes into contact with the hole edge and then uniformly bends the latter over and thus draws it into the hollow profile interior. The entire production apparatus for producing the rim hole is further simplified to a considerable extent by combining the functions of two tools, namely the drawing-in tool and the perforating tool, in the perforating punch.
In a further preferred development of the invention, the hollow profile material of the hollow profile section is drawn into a recess of the tubular piece, this recess encircling in an annular manner and being open toward the end face of said tubular piece. On account of the drawing-in in this way, part of the tubular piece forms a center section of the rim hole. This may be done to such an extent that, with a relatively small drawing-in length, the drawn-in hollow profile material serves only to fasten the tubular piece, which fully maintains the function of the rim hole, for example as a bearing in an axle strut. The tubular piece in this case may be made of bronze or plastic, as a result of which it can additionally perform the function of a plain bearing. No large wall thickness of the hollow profile is required in order to hold the tubular piece, as a result of which said wall thickness can be reduced to such an extent that the drawn-in hollow profile material if necessary produces low rigidity and strength. These properties are alternatively provided by the tubular piece, which is relatively thick-walled. The tubular piece may also be made of a light alloy or of a steel material, as a result of which it can likewise be shaped by the internal high pressure forming process.
In a further preferred configuration of the invention, the hollow profile material is drawn in in such a way that it engages behind undercut surfaces of the recess of the tubular piece. In this way, not only is a frictional connection achieved between the hollow profile and the pushed-in tubular piece, as is apparent in the directly preceding development of the invention, but positive locking is also achieved by the catching behind the undercut surfaces of the recess of the tubular piece, so that the tubular piece is held in the hollow profile in an especially reliable manner.
In a preferred development of the invention, the hollow profile is perforated with holes of the same size being formed. As a result of holes of the same size being formed, uniform process control during perforating, and in particular during drawing-in, is ensured. In addition, the control of the tools during the drawing-in operation is simplified, since the same amount of hollow profile material is bent over on both sides of the hollow profile, a factor which produces a uniform drawing-in length and whereby the sequence of movements of the drawing-in tools is identical, so that the latter can be connected to a single control loop.
In a further preferred development of the method according to the invention, the hollow profile is perforated with holes of different size being formed. Furthermore, the larger hole is dimensioned in such a way that its hole edge terminates flush with the inside of the tubular piece. The hollow profile material is drawn in only on the side of the smaller hole, the hole diameter and the hollow profile section having the hollow profile material being dimensioned in such a way that the hollow profile section extends across the entire length of the tubular piece after the drawing-in. In this way, firstly the production process is shortened, since hollow profile material only needs to be drawn in from one side, whereas only the hole is formed on the other side. Secondly, from this one side on which the smaller hole is formed, so much hollow profile material is drawn in that the latter extends at least up to the edge of the larger hole on the other side of the hollow profile. In this case, firstly the tubular piece is reliably enclosed and secondly a rim hole is formed which is completely gapless and level on account of its one-piece configuration. Thus, due to its freedom from discontinuities and its high surface quality, the rim hole is given especially high bending rigidity and strength and also above average slidability properties, so that the rim hole is suitable in an especially effective manner for the use of plain bearings. This special configuration of the invention applies in particular to bushes of large diameter.
The invention is explained in more detail below with reference to several exemplary embodiments shown in the drawings.